The present invention relates generally to hydraulic shock absorber apparatus of the type employing a fluid filled cylinder and piston arrangement. More particularly, the present invention relates to hydraulic shock absorber apparatus wherein resistance to piston travel is regulated by valves associated within the piston and/or fluid passage between a cylinder and an annular reservoir, and/or a tapered bore within the cylinder to facilitate variable resistance loading relative to the piston position.
Conventional piston-type hydraulic shock absorbers and dampers normally include a piston head attached to an input shaft, whereby input forces are axially applied to the shaft and initiate reciprocal movement of the piston head. Reciprocation of the piston head displaces a quantity of hydraulic fluid through a metering port or valve, whereupon the input energy is dissipated by displacing the fluid through the port. The velocity of the reciprocating head, and therefore the quantity of energy dissipated, is controlled by metering the flow of the displaced fluid to a desired rate.
Many arrangements for achieving a valve orifice variable with piston position have been developed. Most of the hydraulic shock absorbers employ piston arrangements which force a low viscosity, petroleum-based, hydraulic fluid through small openings or valves under very high pressure. Such devices may include a circular orifice in the piston through which passes a tapered rod attached to the cylinder, varied depth grooves in the side wall of the cylinder, tapered cylinders in which a fixed diameter piston operates, spring-loaded valves associated with orifices in the piston or tapered cylinders with compressible piston rings. For example, U.S. Pat. No. 4,048,905 issued Sept. 20, 1977, entitled "Variable Orifice Hydraulic Snubber" discloses a piston cylinder hydraulic snubbing device which employs the gap between ends of a piston ring as the valve orifice. The valve orifice, or piston ring gap, is varied by engagement of the ring with a tapered bore in the cylinder. Thus, on a jounce stroke, the piston ring is compressed against the tapered sidewall of the cylinder and closes the ring gap, thereby increasing piston stroke resistance. On the rebound stroke, the piston ring expands against the tapered sidewall of the cylinder, thereby opening the ring gap and reducing hydraulic resistance to the rebound stroke.
A common problem with many hydraulic shock absorbers involves heat, foaming and cavitation of the hydraulic fluid. A commonly employed solution is to pressurize the hydraulic chamber with nitrogen to control vapor pressures and reduce foaming and fade to improve performance. More recent attempts to improve shock absorber performance has led to electronic or computer controlled valving to provide acceptable performance over a wider range of conditions. By employing extrinsic controls, the reliability and cost of the shock absorber become significant factors in the selection of a suspension system.
Accordingly, a substantial need has been recognized to provide a shock absorber apparatus which, under most circumstances eliminates the need for gas pressurization of the hydraulic cylinder as well as for extrinsic controls over the suspension. In its place, the present invention offers a hydraulic shock absorber which employs an elevated viscosity fluid as the dampening medium and a unique piston construction which utilizes peripheral valving to shunt the fluid between the peripheral edge of the piston and the cylinder wall.